A multimeter (preferably a digital model, with an accuracy of two decimal
places)

A magnifying glass (if necessary)

Before you actually start to mod, you should measure the default voltage of
your card first. Locate the area outlined in the picture below.

That's where you will need to measure the GPU's voltage. Remember, you will
need to do this with your system turned on.

Let's take a closer look at that area. See the two labeled points? To measure
the GPU voltage, you need to connect your multimeter's positive point to either
point A or point B; and connect the negative point to a ground point.

You can either use your computer case or the Molex power connector's ground
wire as the ground point. I personally prefer the Molex connector's ground wire
because I can just poke the multimeter's negative point into the Molex connector
and leave it there.

The GPU's voltage will usually be around 1.6V to 1.7V.
But you must find out your card's exact GPU voltage before you mod it.